Duct Sealing in Existing Nonresidential Buildings

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Duct Sealing in Existing Nonresidential Buildings

• Statewide Codes Standards ProgramPrepared for
  CEC Workshop July 18th, 2002Presentation by
  PGE/HMGJon McHugh, HMG

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Existing Buildings - Duct Testing and Sealing
upon Replacement

• Ducts that are outside of conditioned spaces or
  indirectly conditioned spaces
• ..and attached to single zone AC or HP
• Must be tested and sealed to maximum of 10
  leakage, when
• More than 25 of Duct Surface is replaced, or
• Attached HVAC unit is replaced

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Insulation of Ducts upon Duct Replacement

• Outside of conditioned spaces and attached to
  single zone AC or HP
• ? Must be insulated to R-8
• ? If ducts are outdoors, they must have surface
  reflectance greater than 80

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Duct Leakage in Existing Buildings

• 350 Light Commercial Duct Systems tested for SCE
• 85 of systems needed duct sealing
• Average combined (supply return) duct leakage
  of 36
• Some data indicates that duct leakage
  depressurizes buildings

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Opportunity to Plug the Energy Leaks

• 140,000/year replacement HVAC units installed in
  light commercial buildings
• LBNL study - 65 of ducts in locations where they
  should be sealed
• 140,000 x 0.65 x 0.85 74,000 systems/yr
• Replacing equipment affects the duct/air handler
  seal - opportunity to upgrade duct tightness.

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Prototypical existing building

• 2,000 SF prototype office building
• 9 ft ceiling height, 3 ft plenum height
• Tilt-up wall construction
• No economizer
• 6 ton cooling system
• R-4.2 duct insulation
• Untested Ducts 36 leakage
• Tested sealed ducts 10 leakage

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TDV (Time Dependent Valuation) Savings Results

• DOE2.2 simulation ?hourly energy results
• Hourly energy multiplied by TDV energy factors
• Higher TDV factors on hot weekday afternoons
• Present value of savings 30 year period of
  analysis, 3 real discount rate
• TDV savings TDVbase - TDVproposed

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Duct sealing vs alternatives, Plenum w/ R-19
Ceiling R-0 Roof
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Duct Sealing Alt - Unvented Plenum with Ceiling
and Roof Insulation
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Unvented Plenum with Sealed Ducts Increase Duct
Insulation
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Average Costs/Savings Estimates

• Costs based on
• Sealing 150/ton 30 for 3d party verification
• SCE duct sealing project
• R4.2 to R-8 insulation incremental cost 122
• Owens-Corning Fiberglass
• Weighted TDV savings based upon
• 60 vented plenum, ceiling only insulation
• 40 unvented plenum, both ceiling and roof are
  insulated
• Fans cycled in half of systems

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Prototypical Cost/Benefits
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Benefits from Duct Sealing

• Annual Energy Savings from Sealing Ducts
• Natural gas savings 70,000 MMBtu/yr
• Electricity savings 57 GWH/yr
• Peak demand savings 43 MW
• 10 Years of Savings
• 3.8 Million MMBtu natural gas
• 2,685 GWH electricity
• 430 MW Peak Demand

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Single Zone AC or Heat Pump Replacement

• Ducts tested and sealed to 10 of fan flow
• IF
• Ducts outside conditioned space, or
• In vented plenum, or
• Above insulated ceiling

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Alternatives to Duct Sealing upon Replacement of
Single Zone AC

• For buildings with no roof insulation
• Insulate roof TO R-19 and seal roof vents, or
• Insulate roof TO R-10 and apply cool roof
  coating to roof and any exposed ductwork
• For buildings with roof insulation greater than
  R-5
• ADD R-10 roof insulation and cool roof coating
  to roof and any exposed ductwork

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New or Replacement Ducts Added to Existing Single
Zone AC

• If outside of the conditioned space (above
  insulated ceiling, vented plenum etc)
• Insulated to R-8
• Exposed (outdoors) ducts have a surface
  reflectance greater than 80
• Sealed and tested to lt10 leakage,
• If new or replacement ductwork is greater than
  25 of duct system surface area